The present invention relates to a hydraulic circuit of a loader to which at least a bucket, an arm, and an optional attachment are attached.
A technology of this type is recited in Patent Literature 1 (Japanese Unexamined Patent Publication No. 2011-208693), for example. A hydraulic circuit of a loader recited in Patent Literature 1 is arranged in such a way that, in an unloading passage connected to a hydraulic pump, a boom-operating direction switching valve, a bucket-operating direction switching valve, and a service valve are provided in series in this order from the upstream. The boom-operating direction switching valve is a valve for operating a boom cylinder, whereas the bucket-operating direction switching valve is a valve for operating a bucket cylinder. The service valve is a valve for operating an optional cylinder.